Method for controlling the moisture content of linen leaving a drying ironer and drying-ironer implementing this method

ABSTRACT

To control the moisture content of linen leaving a drying ironer, this content is measured by means of a sensor ( 18 ). The measurement signal is then transmitted to a variable gain amplifier ( 30 ). A circuit ( 32 ) automatically adjusts this gain so that the signal leaving the amplifier ( 30 ) is non-saturated. This gives instant control of linen moisture content irrespective of the moisture content of the items of linen entering the machine.

TECHNICAL FIELD

[0001] The invention chiefly concerns a method for controlling themoisture content of ironed items of linen leaving a drying ironer.

[0002] The invention also concerns a drying ironer using this method,that is to say a drying ironer incorporating means able to maintain themoisture content of the ironed linen at a set value. If the linen comesfrom hospitals for example, the set value is sufficiently low toguarantee good microbial quality of the ironed linen, irrespective ofthe moisture content of the linen on entering the machine.

PRIOR ART

[0003] In a drying ironer, the items of linen to be ironed are placedbetween a rotating ironing roll and a complementary part which fitsaround the contour of part of the roll circumference. Heating meansproduce steam from the water contained in the linen pressed betweenthese parts.

[0004] Drying ironers may be classified in two categories: “calender”drying ironers and “heating roll” drying ironers.

[0005] In calender drying ironers, the rotating ironing roll is linedwith padding and is equipped on the inside with means to collect thesteam and gases released by the linen. The linen items circulate betweenthe roll padding and a metal tray called a “calender”. The heating meansare generally integrated in this metal calender.

[0006] In drying ironers with a heated roll, the heating means arepositioned inside the metal roll whose outer surface is smooth and indirect contact with the linen. The items of linen circulate between theroll and endless fabric belts which are applied against the outersurface of the roll over part of its circumference. Aspiration means areprovided behind the endless belts to collect steam and gas.

[0007] Regardless of the type of drying ironer used, the moisturecontent of the ironed linen leaving the machine depends upon numerousfactors such as the type of fabric, its moisture content when enteringthe machine, the speed with which it passes through the machine, theheating temperature of the linen, etc.

[0008] If the linen to be ironed comes from a hospital for example itmay contain bacteria. The speed of development of these bacteria isgreater the higher the moisture content of the dried, ironed linen. Toguarantee good microbial quality of the linen leaving the drying ironer,it is therefore highly advisable that its moisture content should be aslow as possible.

[0009] Conversely, heating of the linen must not be allowed to exceed acertain value, beyond which there is a risk of burning the items to beironed.

[0010] In most current machines, there is no device with which tocontrol the moisture content of the ironed linen. Users of thesemachines are therefore obliged to manually adjust the linen travel speedand the heating temperature in relation to the type of fabric and itsmoisture content on entering the machines. For practical reasons, thisadjustment made at the start of an ironing cycle which may be long isgenerally not changed until the end of this cycle.

[0011] It will be understood that such single, manual adjustment cannotguarantee good microbial quality of all the items of linen leaving themachine. To avoid burning the linen, the user is naturally prompted tomake an adjustment such that only the items of linen of small size andin synthetic material have a satisfactory moisture content in thisrespect.

[0012] Document DE-A-34 36 553 describes a drying ironer in which theitems of linen circulate between several sets of calender rolls placedin series. Each of the rolls is rotary driven at adjustable speed andcomprises steam suction means fitted with a throttle valve with anadjustable opening. On leaving the machine, the items of linen areplaced on a metal plate and their residual moisture content is measuredbetween said plate and a point contact part by means of a Wheatstonebridge. The moisture content so measured is compared with an adjustableset value.

[0013] If the measured moisture content is higher than the set value,the throttle valve of the suction means of the first roll-calenderassembly is opened gradually in the direction in which the linentravels, then the valve of the suction means of the second roll-calenderassembly is opened and so forth until the desired moisture content isreached. If the moisture content still remains too high after fullyopening all the throttle valves, the speed of rotation of all the rollsis reduced.

[0014] Conversely, if the measured moisture content is lower than theset value, the throttle valve of the last roll-calender assembly isgradually closed in the direction in which the linen travels, then thesecond to last assembly and so forth until the set moisture content isreached. If the measured moisture content remains lower than the setvalue after all the throttle valves have been closed, the rotation speedof all the rolls is increased.

[0015] The means for controlling the linen drying rate described in thisdocument raise problems which make these means inefficient in practice.

[0016] The source of the first problem raised is to be found in thegraph illustrated in FIG. 1 of the appended drawings, showing thevariations in equivalent electric resistance (in Ohms) of an item oflinen in relation to its moisture content. It can be seen from thisgraph that very small variations in this content lead to very largevariations in equivalent electric resistance when the linen is not verymoist (moisture content less than 6%). Conversely, when the linen isvery moist (moisture content higher than 15%), the equivalent electricresistance of the linen is practically constant. Under these conditions,it does not appear possible in practice to control the moisture contentof the linen directly on leaving the machine by means of a measurementmade by a Wheatstone bridge of invariable characteristics as taught bydocument E-A-34 36 553.

[0017] Another disadvantage of the drying control means described inthis document derives from the fact that the resistance of each item oflinen is measured by causing it to pass between a metal plate and apoint contact part. The measurement therefore undergoes substantialvariations, in particular on account of full or partial electric contactlosses between the contact part and the linen. These contact losses meanthat the measurement made is practically impossible to use.

[0018] A further disadvantage of the control means described in documentDE-A-34 36 553 derives from the fact that adjustment of the moisturecontent is made in priority by controlling steam suction. Theconsequence is a relatively long response time, incompatible with goodmicrobial quality of the linen leaving the machine.

DESCRIPTION OF THE INVENTION

[0019] The subject of the invention is precisely a method forcontrolling the moisture content of linen items leaving a drying ironer,with which it is possible to solve, at least in part, the problems ofthe drying ironers of the prior art, in particular by ensuring effectivecontrol of the moisture content of the ironed linen, even when thiscontent undergoes substantial variations during one same ironing cycle.

[0020] In accordance with the invention, this problem is solved using acontrol method for the moisture content of ironed linen items leaving adrying ironer, according to which the moisture content of the ironedlinen items is measured, then at least one element of the drying ironeris monitored according to the measured moisture content, so that it canbe moved towards a set value, characterized in that the measuredmoisture content is amplified with an instant optimised gain so that themeasured moisture content so amplified has a non-saturated value, whichis used to monitor said element of the drying ironer.

[0021] By means of this method, the amplification gain is automaticallyadjusted in relation to the value of the measurement signal, so as toobtain a non-saturated output signal which can then be used to correctthe moisture content of the linen leaving the machine. Efficient,practically instantaneous adjustment of this content is thereforeobtained irrespective of the moisture content of the linen when placedin the drying ironer.

[0022] Advantageously, a maximum value is given to the gain, then thegain is divided by a given factor, as many times as necessary, until themeasured, amplified moisture content shows said non-saturated value.Preferably, the dividing factor is given a value that is substantiallyequal to two.

[0023] If no measurement is made of the moisture content of an ironeditem of linen, that is to say when no item of linen leaves the machine,the optimised instant gain is advantageously kept unchanged for apredetermined length of time after the end of the measurement of thelast item of linen ironed. With this characteristic, it is possible toavoid recommencing measurements using the maximum gain value whenseveral items of linen are ironed one after the other.

[0024] Further advantageously, several moisture content measurements aremade successively, the measurement signals are smoothed and the averageis calculated before they are amplified with said instant optimisedgain. With this characteristic it is possible not to take into accountany abnormal measurements when controlling the moisture content of thelinen.

[0025] A further subject of the invention is a drying ironer comprisingmeans for measuring the moisture content of ironed linen items leavingthe drying ironer, said measurement means being able to deliver ameasurement signal in the presence of an item of linen, and controlmeans that are sensitive to the measurement signal so as to adjust themoisture content by acting on at least one element of the drying ironer,characterized in that the control means comprise means for variable gainamplification of the measurement signal and means for automatic gainadjustment able to give the gain of the amplification means an optimisedvalue, so that the amplification means emit a non-saturated outputsignal.

[0026] According to one preferred embodiment of the invention, theelement on which the control means act is a means for adjusting thespeed of travel of the linen items in the drying ironer. Theseadjustment means can in particular vary the rotation speed of theironing roll in the machine.

[0027] Preferably, the means for measuring the moisture content comprisetwo electrically conductive parts each comprising at least two(preferably five) flexible tongues able to be placed simultaneously incontact with the items of linen leaving the drying ironer, the flexibletongues of both conductive parts being arranged in alternate manner soas to form as many element sensors as there are pairs arranged inparallel.

[0028] Advantageously, the machine also comprises means for measuringthe moisture content of the linen items to be ironed on entering thedrying ironer.

[0029] Preferably, the machine also comprises means for recording themeasurement signal to provide maximum traceability of the ironed linen.

SHORT DESCRIPTION OF THE DRAWINGS

[0030] As a non-limitative illustration, a preferred embodiment of theinvention is described below with reference to the appended drawings, inwhich:

[0031]FIG. 1, already described, shows the changes in equivalentresistance (in Ohms) of a linen item in relation to the its moisturecontent (%) for a given value of the signal amplification gainrepresenting this resistance; and

[0032]FIG. 2 is a very schematic diagram of a drying ironer according tothe invention, equipped with means for controlling the moisture contentof ironed linen;

[0033]FIG. 3 is a perspective view which, on a larger scale, illustratesthe means for measuring the moisture content on leaving the machine; and

[0034]FIG. 4 is a schematic diagram of the control means fitted to themachine in FIG. 2.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0035]FIG. 2 is a very schematic diagram of a drying ironer with aheated roll fitted, according to the invention, with means forcontrolling the moisture content of ironed linen items leaving thismachine. However, persons skilled in the art will understand that theinvention is not limited to this type of machine and also concernscalender drying ironers.

[0036] In the case shown of a drying ironer with heated roll, FIG. 2shows an ironing roll 10, having a horizontal axis, means 12 (such as anelectric motor) to drive roll 10 in rotation around its axis, atadjustable speed, and endless fabric belts 14, in contact with part ofthe circumference of roll 10. The endless fabric belts are mounted onrollers such as 16 whose axes are parallel to the axis of roll 10.

[0037] To facilitate the reading of FIG. 2, some component parts of thedrying ironer, well known to persons skilled in the art, have not beenshown. Among these components in particular are the heating meanspositioned inside roll 10 and means for aspirating the gas and steamreleased by the linen through the fabric belts 14.

[0038] Ironing of the item linens is made by placing the latter betweenroll 10 and the fabric belts 14 in a direction corresponding to thedirection of rotation of roll 10 (arrow F). The ironed, dried linenitems leave the machine via a cylindrical, substantially horizontal part14 a of fabric belts 14.

[0039] In accordance with the invention, the drying ironer schematicallyshown in FIG. 2 integrates a device with which it is possible tocontinuously control the instant moisture content of linen items leavingthe machine, so that this content is permanently maintained at a setvalue irrespective of the moisture content of the linen items whenentering the machine. More precisely, the set value is chosen to besufficiently low to guarantee good microbial quality of the ironedlinen, in particular hospital linen.

[0040] As will be described more in detail below with reference to FIG.4, the device for controlling the moisture content of ironed linen itemschiefly comprises means 18 for measuring this moisture content and means20 for monitoring at least one element of the drying ironer able toadjust this content.

[0041] The measuring means 18 are positioned at the exit of the dryingironer, precisely above the cylindrical substantially horizontal part 14a of the fabric belts 14, in the illustrated embodiment. They aredesigned to deliver a measurement signal representing the moisturecontent of the ironed linen items leaving the machine.

[0042] In the preferred embodiment of the invention illustrated in FIG.3, the measuring means 18 comprise two electrically conductive parts 21and 22, electrically insulated from one another by an insulating block24.

[0043] More precisely, the electrically conductive parts 21 and 22 aremetal plates. These plates comprise substantially flat base parts 21 aand 22 a which are mounted on a fixed part 26 of the machine, above thecylindrical substantially horizontal part 14 a, so that they aresubstantially parallel to one another.

[0044] Each of the metal plates forming the electrically conductiveparts 21 and 22 also comprises at least two flexible tongues 21 b and 22b, which project beyond the base plates 21 a and 22 a. The flexibletongues 21 b and 22 b are arranged parallel to each other in alternatefashion and are equidistant from one another. Their end parts are foldedalong the same plane, tangent to the cylindrical substantiallyhorizontal part 14 a via which the ironed linen items exit from themachine. Therefore, the ironed linen items leaving the machine aresimultaneously in contact with all the end parts of flexible tongues 21b and 22 b.

[0045] In the preferred embodiment of the invention illustrated in FIG.3, each of the metal plates forming the electrically conductive parts 21and 22 comprises five flexible tongues 21 b and 22 b.

[0046] The arrangement of the measuring means 18 just described meansthat at least two and preferably five moisture sensors are formed andarranged in parallel. In this manner a relatively low measurement valueis given to the sensitivity of the measuring means, well adapted to themeasurement of the very low moisture content generally found at the exitpoint of drying ironers.

[0047] As illustrated in FIG. 4, electric conductors 28 connect the twoelectrically conductive parts 21 and 22 of measuring means 18 to thecontrol means 20. These electric conductors 28 convey an electricmeasurement signal, representing the electric resistance between theelectrically conductive parts and, consequently, the moisture content ofthe linen item which may be in contact with tongues 21 b and 22 b.

[0048] In accordance with the invention, the control means 20 comprisevariable gain amplification means 30, for amplifying the measurementsignal derived from measuring means 18.

[0049] According to the invention, the control means 20 also comprisemeans 32 for automatically adjusting the gain of amplification means 30.These means 32 for automatic gain adjustment are arranged such that theycan give an instant optimised value to the gain of the amplificationsmeans 30, so that the output signal emitted by the amplification means30 is non-saturated irrespective of the moisture content of the linenitems leaving the machine.

[0050] In other words, at each instant the means 32 for automatic gainadjustment determine an instant optimised gain for which the outputsignal delivered by the amplification means has a usable value at alltimes, that is to say separate from the saturation limits for whichvariations in the moisture content of the linen do not cause the signalleaving the amplification means to vary.

[0051] The control means 20, at the exit of the amplification means 30,therefore deliver a signal which is permanently reflects the moisturecontained in the linen items leaving the machine, irrespective of thismoisture value.

[0052] In practice, the means 32 for automatic gain adjustment may inparticular integrate an algorithm which calculates the instant optimisedgain from the measurement signal delivered by the measuring means 18.

[0053] In the preferred embodiment of the invention, but without beinglimited thereto, the automatic gain adjustment means initially give themaximum value to the gain of the amplification means 30.

[0054] If the output signal of these means is non-saturated, this gainvalue is taken as the instant optimised value and is maintained for aslong as the output signal remains non-saturated.

[0055] Conversely, if the output signal of the amplification means issaturated, the means 32 for automatic gain adjustment divide the maximumgain value by a predetermined factor, for example substantially equal to2 in the preferred embodiment of the invention.

[0056] It is then checked again whether or not the output signal fromthe amplification means 30 is saturated. If not, the maximum gain valueafter dividing by said factor is taken as the instant optimised valuefor as long as the output signal remains non-saturated. If this is notthe case, the last gain value is again divided by the said factor and soforth until an output signal is obtained which is non-saturated.

[0057] The non-saturated output signal so obtained according to theinvention, is then compared at 33 with a set moisture content value andused to monitor one ore more elements of the drying ironer able toadjust said content. In the preferred embodiment of the inventionillustrated in the figures, this element is the means 12 for drivingroll 10 in rotation. More precisely, action is exerted upon thesedriving means 12 so as to adjust the moving speed of the linen items inthe machine. The effect of this adjustment is to bring the moisturecontent of the linen items leaving the machine to the required set valuevery quickly.

[0058] To complete the description, it is to be noted that before itsinjection into the amplification means 30, the measurement signalpreferably undergoes a smoothing operation in a smoothing circuit 34 andan averaging operation in an averaging circuit 36. Therefore, themeasurement signal transmitted to the amplification means 30 does nottake into account any erratic measurements and represents the average ofa determined number of consecutive measurements.

[0059] In addition, in the preferred embodiment of the invention, thealgorithm of the means 32 for automatic gain adjustment is designed sothat amplification does not need to be systematically recommenced with amaximum gain value when several linen items from one same batch andhaving substantially the same moisture content are ironed withoutinterruption one after the other.

[0060] For this purpose, when the measuring means 18 do not emit anymeasurement signal indicating the presence of a linen item on thecylindrical substantially horizontal part 14 a, the algorithm maintainsthe last instant optimised gain value unchanged for a predeterminedlength of time after the end of the preceding measurement signalindicating the presence of a linen item on part 14 a.

[0061] Advantageously, the drying ironer of the invention is also fittedwith means 38 for measuring the moisture content of linen items to beironed placed in the drying ironer (FIG. 2). These measuring means 38may be produced in the same manner as the measuring means 18 previouslydescribed. They are mounted on another fixed part 40, above anothercylindrical substantially horizontal part 14 b of endless belts 14,located at the point where the linen items are placed in the machine.

[0062] The signal delivered by measuring means 38 is also transmitted tothe automatic gain adjustment means 32 (FIG. 4). It may be used inparticular to detect the placing of an item of linen in the dryingironer.

[0063] As schematically shown in FIG. 4, the measurement signaldelivered by the measuring means 18 positioned at the exit of themachine is advantageously recorded in recording means 42 with otherdata, used in particular to identify the ironed linen items. With thisarrangement, it is possible to ensure the traceability of the operationsconducted on the machine and more precisely to guarantee good microbialquality of the ironed linen.

[0064] Evidently, the invention is not limited to the embodiment justdescribed by way of example. For example, the algorithm used toautomatically adjust the gain of the amplifications means 30 to theinstant optimal value may be substantially different from the onedescribed. In particular, this algorithm may initially give the gain itslowest value or a preset average value. Also, the means for measuringthe moisture content may in some cases be replaced by existing meanswhile remaining within the scope of the invention.

1. Method for controlling the moisture content of ironed linen itemsleaving a drying ironer, according to which the moisture content of theironed linen items is measured, then at least one element of the dryingironer is monitored according to the measured moisture content, so thatit can be moved to a set value, wherein the measured moisture content isamplified with an instant optimised gain so that the measured moisturecontent so amplified shows a non-saturated value, which is used tomonitor said element of the drying ironer.
 2. Method according to claim1, in which the gain is initially given a maximum value, then the gainis divided by a given factor, as many times as necessary until themeasured, amplified moisture content shows said non-saturated value. 3.Method according to claim 1, in which, if no measurement is made of themoisture content of an ironed item of linen, the instant optimised gainis kept unchanged for a predetermined length of time after the end ofthe measurement of the moisture content of the last item of linenironed.
 4. Method according to claim 1, in which successive measurementsof the moisture content are taken, the measurement signals are smoothedand their average is calculated before they are amplified with saidinstant optimised gain.
 5. Drying ironer comprising means for measuringthe moisture content of ironed linen items leaving the drying ironer,said measuring means being able to deliver a measurement signal in thepresence of an item of linen, and control means sensitive to themeasurement signal so as to adjust the moisture content by acting on atleast one element of the drying ironer, wherein the control meanscomprise variable gain amplification means for amplifying themeasurement signal, and means for automatic gain adjustment able to givean optimised value to the gain of the amplification means so that theamplifications means emit a non-saturated output signal.
 6. Dryingironer according to claim 5, in which the automatic adjustment meansinitially give the gain a maximum value, then divide the gain by a givenfactor, as many times as is necessary, until said optimised value isobtained.
 7. Drying ironer according to claim 5 in which, in the absenceof a measurement signal, the automatic adjustment means maintain thegain at said optimised value for a predetermined length of time afterthe end of the last measurement signal.
 8. Drying ironer according toclaim 5, in which the control means comprise smoothing means andaveraging means.
 9. Drying ironer according to claim 5, in which theelement on which the control means act are means for adjusting theconveying speed of the linen items in the drying ironer.
 10. Dryingironer according to claim 5, in which the means for measuring moisturecontent comprise two electrically conductive parts each comprising atleast two flexible tongues able to contact simultaneously the items oflinen leaving the drying ironer, the flexible tongues of the twoconductive parts being arranged in alternate manner so as to form asmany element sensors as there are pairs arranged in parallel.
 11. Dryingironer according to claim 5, also comprising means for measuring themoisture content of linen items to be ironed entering the drying ironer.12. Drying ironer according to claim 5, also comprising means forrecording the measurement signal.